The first provisional headquarters were on the road Carrer Provença in the office of the lawyers who oversaw the legal proceedings. They moved to Via Laietana 28, to the same building as the US Consulate, a year later. The number of IEN members began to grow little by little, and the organization equipped future headquarters thanks to their donations. The increase in activities caused it to outgrow the premises and it moved again in 1956, this time to Carrer València, where there was an office and a conference room. As it continued to grow, it once more outgrew the premises, so the organization rented a second space on Passeig de Gràcia, with one being used for cultural activities and the other for English classes.
The growing success of these activities and English classes led to the decision to construct a large building on a plot on Via Augusta 123 which it inaugurated in 1961 with an official financial contribution from the US government. The building has seven floors and a basement, as well as an almost 300-seat theater and a large open-air patio.
The facade, designed by Josep Mª Bosch i Aymerich himself, is noteworthy for its originality and has not lost value over time.
The organization built an annex on Carrer Sant Eusebi in 1971, where the library is now located.
American English has been taught at the IEN from the outset. In-person classes have always taken place with native teachers and no more than fifteen students per class. The official programs began in the 1960-61 academic year and, thanks to the large number of classrooms available in the building on Via Augusta, the Institute could offer programs specific to children, teenagers and adults from an introductory level up to proficiency (C2 level). The programs were adapted to the methodological strategies of the moment and the most modern teaching technologies were progressively incorporated.
During these 60 years, over 400,000 students took classes at the IEN and it is uncommon to find someone who does not remember their time as an English student there. The long queues that formed along the street at every registration have become famous. The American English teaching program finished in June 2019, when doors opened up to other academic activities geared toward North American studies.
Inaugurated in 1982 by Ambassador Terence Todman, it contains more than 10,000 American books and has been a benchmark to discover American authors and publications from all areas of culture, economics, history, politics and the workings of American institutions. As a benchmark library, it has served to document different studies and reports.